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Three comparable ecosystems
Three different ecosystems:
The Benguela Current | The Canaries Current | The Humboldt Current
Modelling, GIS, acoustic observation...
The Humboldt Current
The Humboldt Current system with its permanent upwelling cells off Peru, and seasonal upwelling along the coasts of Chile, is by far the most productive in fish landings. With less than 1% of the world’s ocean surface, it provides 15 to 20% of world marine catches (up to nearly 20 million tons per year for Peru and Chile combined). A second particularity lies in the presence of a very intense, extensive shallow zone, very low in oxygen. Its final particularity is its position under the direct influence of the ENSO mechanism (El Niño Southern Oscillation).
Scientists have put forward the hypothesis according to which instead of negatively affecting fish populations, ENSO events could be the secret of the extremely high productivity of this ecosystem. Contrary to what has long been accepted, the El Niño phenomena do not have a systematically negative effect on the anchovy and a positive one on the sardine. The impact of these phenomena can only be interpreted by taking into account the system as a whole, on very diverse temporal and spatial scales.
Various hypotheses have been proposed to explain the fluctuations between anchovy and sardine populations observed in the Humboldt system. These hypotheses are linked to some mechanism occurring at different spatiotemporal scales, including fluctuations in climate, oceanographic conditions, planktonic communities (abundance and size ranges), fish behaviour and their available habitat. The major fluctuations in biomass seem to be linked to both a high exploitation rate of some targeted species within the ecosystem and to environmental changes. Fluctuations in abundance are not restricted to anchovies and sardines but concern the whole ecosystem (giant squid, Munidae, Myctophidae, etc.) which shows variability at different scales.
The role of climate fluctuations with a period of approximately 50 years has been the subject of many studies in the Californian and Humboldt Currents. These suggest focusing on decadal scale variability such as ENSO.
